The heater core is in the engine compartment. The labor instructions say the job takes about 2 hours if your Dodge hasn't got air conditioning but the imply if you have air conditioning the air conditioning has to be evacuated and later recharged about 4 hours or so.
Its best to have a workshop manual www.Autozone.com have some free ones one line once you register on thier website.
There is a company that independent auto repair shops "buy" their information from that offer a very reasonable service to do it yourselvers. You get a one year subscription to year make and model specific repair procedures, service bulletins, component locations, wiring diagrams ect.... great quality information same as the professionals have ,much better than generic workshop manuals from parts stores, much cheaper than the factory manual. http://www.alldatadiy.com/